Commercial processes currently available for the production of nuclear grade zirconium are variations of a solvent extraction process wherein zircon sand is converted to zirconium metal as a result of a somewhat involved series of steps. This extraction process requires the use of an organic solvent, usually hexone, and various aqueous solutions, including hydrochloric acid. Hafnium, which is chemically similar to zirconium, must be separated from the zirconium. The hexone/thiocyanate/hydrochloric acid system employed for this purpose requires a series of separate extraction and separation columns. The zirconium, organic solvent and thiocyanate recovered from the hafnium separation steps are usually subjected to additional processing to insure that as much zirconium is recovered from the system as possible. The zirconium ultimately recovered from most extraction processes is in the form of pure zirconium oxide (ZrO.sub.2). In a commonly used commercial process, the zirconium oxide is chlorinated to form ZrCl.sub.4, which is purified and subjected to Kroll reduction to produce zirconium metal suitable for nuclear applications. The aqueous and organic liquids used in the process typically include waste metals and other materials that must be properly disposed of. One of the methods of treating these liquid wastes is to place them in holding ponds for future treatment and remediation. However, this is increasingly becoming an unacceptable waste management solution, particularly since federal and state laws relating to waste disposal have become more stringent.
The solvent extraction processes effectively separate zirconium from hafnium to produce zirconium of the quality required for use in nuclear reactors and elsewhere in the nuclear industry. However, the increasing concern expressed by the public, the scientific community and the regulatory agencies regarding the waste generated by solvent extraction processes has led the nuclear industry to explore alternative zirconium production methods which do not present the same waste management concerns. For example, the hexone-thiocyanate zirconium extraction process can generate offensive odors, and the waste from both the zircon sand chlorination process and the zirconium raffinate precipitation may include potentially toxic materials which must be properly disposed of.
Other zirconium-hafnium separation methods in addition to the aforementioned solvent extraction method have been proposed by the prior art. Ion exchange processes for separating zirconium and hafnium are described in U.S. Pat. Nos. 2,546,953 to Street and 2,759,793 to Lister et al., in British Patent No. 755,601 to Lister et al., and in Belgian Patent Publication No. 602,663. Adsorption processes are disclosed in U.S. Pat. Nos. 2,571,237 to Hansen and 2,860,956 to Arden et al.
In U.S. Pat. No. 2,546,953, Street discloses an ion exchange separation process wherein the mixed oxychlorides of zirconium and hafnium are passed through a cationic exchange resin and then recovered with hydrochloric acid. U.S. Pat. No. 2,759,793 and British Patent No. 755,601 to Lister et al. also disclose a method of separating zirconium from hafnium using a cationic exchange resin. Zirconium and hafnium in soluble salt form, which can include their oxychlorides, are passed through an acidified cation exchange resin and then eluted with sulfuric acid. The Belgian patent publication No. 602,663 discloses an ion exchange zirconium-hafnium separation and recovery method based on sulfate separation chemistry. Not only do these processes not produce a highly pure zirconium, but waste management is still a problem. In particular, each of these processes generates liquid waste which requires proper disposal.
Hansen, in U.S. Pat. No. 2,571,237, discloses the absorption of hafnium from a solution of mixed zirconium and hafnium chlorides with silica gel. Organic solvent containing purified zirconium values is then separated from the absorbent. U.S. Pat. No. 2,860,956 to Arden et al. also employs an organic solvent to extract the zirconium values from an absorbent containing both zirconium and hafnium. Although the aforementioned separation processes effectively separate zirconium in a usable form from hafnium, they do not avoid the waste management concerns associated with solvent extraction processes. The prior art adsorption processes require organic solvents to isolate the zirconium which must be disposed of. Moreover, the unpleasant odors and the other drawbacks that accompany the use of organic reagents are drawbacks to the contemporary use of these processes.
Consequently, the prior art has failed to provide a simple zirconium-hafnium separation process for producing nuclear quality zirconium which eliminates both liquid discharge and organic reagents and which is not accompanied by involved waste management procedures.